An ideal system for identifying disease mechanisms of diabetes and screening for new therapeutics would be a renewable source of beta cells and the ability to study patient-specific cells. Such a system could help identify beta cell-intrinsic mechanisms of cell death in type I diabetes and help establish genotype-phenotype correlations. 2D cell culture systems have been the mainstay of attempts to culture human cadaveric islets or to differentiate human pluripotent stem cells (hPSCs) toward the pancreatic beta cell fate. However, human islets cannot be maintained for prolonged periods of time with these systems, nor can functional beta cells be produced from hPSCs. Since current 2D culture conditions do not take into account critical cell-cell and cell- matrix interactions for beta cell development and function, there is a need for new 3D culture models of human islets that more accurately mimic the in vivo environment. Our multidisciplinary team of a stem cell/islet biologist a vascular biologist and two bioengineers proposes to develop a novel in vitro platform to create a human islet micro-organ perfused with human microvessels in a microfluidic device with all components derived from a single human induced pluripotent stem cell (hiPSC) source. First, we will optimize conditions and cell ratios by creating a 3D in vitro human islet micro-organ in static cultures outside the device that is comprised of islet endocrine cells, stromal cells, pancreas-specific extracellular matrix, and human endothelial cells (Aim 1). Next, we will assemble these 3D human islet micro-organs in a microfluidic device, so that nutrients are delivered and waste products are removed through a perfused capillary bed. This 3D islet micro- organ will closely mimic the dynamic metabolic changes typical for the in vivo beta cell environment (Aim 2). While a hiPSC-derived islet micro-organ is the ultimate goal, we will pursue a parallel approach with each Aim, using human cadaveric islets as a cell source, as experiments with primary human islets will provide important insight into the microenvironment necessary for maintaining mature beta cells ex vivo. Our model, which fully mimics in vivo physiology and is amenable to high throughput screening, will provide a platform for identifying regulators of beta cell maturation, replication, failure, and survival and will help reveal the causes of human diabetes. Our microfluidic platform has the flexibility to combine islet micro-organs with additional micro-organs (e.g. liver) in a continuous vascular network to simulate the complex inter-organ interactions relevant to human beta cell physiology. Thus, our platform will enable studies into the role of inter-organ cross talk in the pathogenesis of diabetes.